1. Field of the Invention
The present invention relates generally to capacitors and, more particularly, to a structural capacitor.
2. Description of Related Art
In many situations it is desirable to create electrical capacitors that can not only store electrical energy, but also simultaneously carry mechanical loads. For example, in military applications, the storage and release of electrical pulsed power is useful in many different applications, such as electromagnetic rail guns, electromagnetic armor, short-pulse high-energy lasers, and the like. Cylindrically wound thin-film capacitors are one technology used to store and release electrical energy.
There have been conventional pulsed power platforms that include components which carry structural loads. For example, continuous fiber-reinforced, polymer-matrix composite materials have been used to create strong, stiff, and lightweight structures, such as vehicle frames and ballistic armor panels.
Gains in overall platform efficiency are possible by creating a laminated composite material that can both carry mechanical loads as well as store and release electrical energy. The previously known designs include metallized polymer film electrodes that are interleaved between glass fiber-reinforced epoxy composite plies with the resulting stack of materials processed together to integrally bond the components together.
In order to form such laminated structural capacitors, the previously known methods include enveloping the materials in an evacuated bag so that the stack of laminated materials is subjected to atmospheric pressure. The bag with the contained stack is then placed in an autoclave, hot press, or convection oven to bond the layers together.
These previously known methods, however, have only been effective to form structural laminated capacitors for a limited number of layers, e.g. no more than about five dielectric layers, since the layers are not laterally confined while being constructed or bonded together. Rather, under the compaction pressure, the layers of material move laterally and lose their relative alignment with each other.
Alignment, however, is the key to both structural and electrical operation since the alignment and relative position of the layers determines both the laminate stiffness and strength as well as the energy density and capacitance of the capacitor. In some cases, the lateral shifting of the layers may result in misalignment of electrodes so that opposing electrodes are in direct contact with each other. This, in turn, shorts the capacitor rendering it inoperable.
Other methods, such as closed molds and adhesive tape, have also been tried to limit lateral movement of the layers when constructing and bonding the layers of the structural capacitor together. These previously known attempts, however, have not proven successful except for only a limited number of layers of the capacitor. The limited number of capacitor layers, in turn, limits not only the structural strength of the capacitor, but also the capacitance and amount of energy which can be stored by the capacitor.